Current databases are typically designed for the storage and interface characteristics of hard-disk devices. An alternative form of storage device, however, is a flash device. While flash-based storage devices were not common in previous databases, recent technology improvements in flash device storage capacities have made the use of flash devices in databases more feasible. The increasing use of mobile and low power devices further motivates the use of flash devices in such mobile devices because hard disks may be prohibitively heavy or energy intensive.
A key feature of flash storage devices is that their characteristics vary depending on the interface used to access the flash device. A flash device may be accessed through many different interface types, such as in a USB (Universal Serial Bus) stick, in a compact flash card, a secure digital (SD) card, a mini-SD card, a micro-SD card, or in a printed circuit board of a mobile or embedded device. While speed of data transfer across the interface may not be a bottleneck, differences exist in the nature of low level flash management implemented behind the interface by the flash device manufacturer. The performance of the flash-based database and the underlying indexing algorithm depends on the characteristics of the flash device as observed through each specific interface.
There are many applications where it is desirable to store data within a sensor network, rather than transmit the data to a central database. Example applications include remote deployments where an economical communication infrastructure is not available, mobile sensor nodes with sporadic and short-lived connections, and sensor networks of mobile devices which have significant local processing power.
In many cases where data storage is part of a sensor network, flash-based storage devices are commonly used rather than hard disks due to their more favorable characteristics, including shock resistance, node size, weight, and energy considerations. Additionally, flash is also common in many mobile devices such as personal data assistants (PDAs), cell phones, music players, and personal exercise monitors. These devices may greatly benefit from the favorable characteristics of flash memory.
Existing database products, however, are typically designed for hard disks, and may therefore suffer from drawbacks when using flash devices. For example, such database products are typically not optimized for flash device characteristics, and unlike many traditional database applications, may be used in various applications for which the workload is highly write intensive. Indexing schemes have been proposed to address these concerns, however, existing indexing schemes are not optimized for many available flash devices or for many realistic workloads. In this way, existing indexing schemes may not be suitable in many practical systems, especially when the systems are designed to be highly flexible and capable of handling multiple types of workloads.